This invention relates to a hydraulic control system for a roof support assembly of an underground mining installation.
A known type of roof support assembly is constituted by a plurality of identical roof support units positioned side-by-side along, for example, a longwall face. Each unit is provided with hydraulic advance ram means so that the units can be advanced individually, or in groups, to follow the advance of the mineral face being won. Such an assembly is known as a walking frame roof support assembly. Each roof support unit is typically constituted by a floor sill, a roof cap and a goaf shield, the roof cap being supported by hydraulic props which rest on the floor sill. Such a roof support assembly is provided with a hydraulic control system which is used to control the various operations of each of the units of the assembly, such as the retraction of the props prior to the advance of a unit, advance of that unit, and extension of the rams after the advance. The control system may be operated manually by either proximity or remote control, and the units may be controlled either individually or in groups.
Although the known hydraulic roof support control systems have proved quite reliable in practice, they do suffer from a number of disadvantages. In particular, when the props of a given roof support unit are retracted, the extent of this retraction depends entirely upon the degree of control exercised by the operating personnel. Consequently, there is a danger that, as the roof support units are advanced, the props are forcibly retracted to too great an extent. This is particularly dangerous when mining seams of small thickness. In the extreme case, the roof cap of a unit may be lowered to such an extent that, if sufficient attention is not paid, the face workers might suffer serious, or even fatal injuries by being crushed between the downward moving roof support parts and the floor of the working.
However, even where seams of large thickness are being mined, the roof caps of the roof support units may be lowered to an unnecessary extent during the advance operation. For example, if the roof caps of adjacent units bear against one another for guide purposes, their supporting and guiding functions may cease if the roof caps are lowered too far, so that considerable working difficulties can arise.
The aim of the invention is to provide a control system for a hydraulic roof support assembly which does not suffer from the disadvantages outlined above.